A circuit card is the current state of the art for building assemblies of electronic devices including a plurality of integrated circuits (“chips”). These assemblies can be separated into multiple types: organic multilayer laminated printed wire board (PWB), low temperature co-fired ceramic (LTCC), and high temperature co-fired ceramic (HTCC). Using each of these technologies, circuit card assemblies have been fabricated.
In a superconducting supercomputer, many of the operating processing integrated circuits (“chips”) are cooled to about 4 K, but certain of the memory chips instead have a much warmer operating temperature of about 77 K. Providing cooling at 4 K is a costly activity, so every effort is made in superconducting supercomputer design to reduce the thermal parasitic load. This includes placing the assembly in vacuum (no convection), use of coatings and multilayer insulation to reduce thermal radiation, and limiting the conductive thermal load between the “hot side” and “cool side” of the entire assembly.
For large scale applications, the state of the art currently solves the problem of achieving the desired operating temperatures for a superconducting supercomputer by utilizing a large centralized refrigeration plant. Such a system supplies liquid coolant (helium at 4 K or nitrogen at 77 K). The thermal parasitic load is minimized by using separate cryogenic vessels or dewars for each of the temperature regimes. A 4 K dewar is maintained with liquid helium and a 77 K dewar may contain liquid nitrogen. Signals between the two temperature sides are completed by cabling. This solution requires cables that are long from a digital perspective, which results in significant latency between the 4 K and 77 K regions and may require more parts in the 4 K stage. These additional parts consume significant power and make certain designs of superconducting supercomputers infeasible.
In small scale applications, a cryocooler or closed cycle refrigerator can be used to provide cooling at both temperatures. By this method, the first stage of the cryocooler provides an approximate 77 K platform while the final stage of the cryocooler provides a 4 K stage. Connections between the two zones are completed by cabling. While this brings the two temperature sides closer together, this approach is not scalable to large applications because the heat removal of the cryocooler is insufficient.